MC3 UCB1400: modify code/filter to reduce jitter

On MC3 with UCB1400 resisitive touch we see huge amounts of noise on the analogue touch-signals - esp. when evaluating sampling x-coordinates - due to crosstalk from the display signals running over the same cable. This causes lots of jitter in the touch-coordinates reported, esp. for a brief moment after each touch-down.

This patch modified the code to discard the first few samples after each touch-down, ignore (and immediately retry) samples, when too much noise is recognized, and tweak the filters to reduce the jitter.

BCS: 746-001399